Penn insists his onscreen sister is just misunderstood and is acting like a typical teenager. What do you think, BFFs?

Taylor Momsen has been an active member of the Brat Pack in recent months, dissing other celebs like Justin Bieber, Rihanna and Miley Cyrus, chain-smoking cigarettes, admitting to burning her dog’s balls, calling her band, The Pretty Reckless, the last remaining ‘authentic’ rock group and has even said she doesn’t get along with her fellow Gossip Girl cast members! However, her onscreen big brother, Penn Badlgey, says that Taylor is totally misunderstood and simply acting her age!

“First of all, it’s not true [that Taylor doesn’t hang out with the rest of the cast],” the 23-year-old Easy A star star told HollywoodLife.com exclusively at In Touch Weekly‘s post-VMAs party Sept. 12. “[My girlfriend Blake Lively] and I saw her the night she did Letterman, and we hung out with her in her hotel room. It was a very calm night – she wasn’t crazy partying or anything like that.

“Taylor’s a teenager, and teenagers go through what they’re going to go through,” he added. “It just so happens that she’s in the eye of the press, and I think that’s unfortunate, because everyone should be allowed to make their mistakes. I think it’s like, she’s 17. Give her time. She’s a really sweet girl, very smart, very talented. She’s just growing up.”

Penn is also supportive of Taylor’s future as a singer. “I saw her perform a year ago, but I haven’t seen her recently. She had a great presence [back then] and I think she’s very talented. She loves music, and as long as she’s doing what she loves, that’s something I respect.”